1. Field of the Invention
This invention relates to an actuator element, and more particularly to an ultra-small actuator element wherein an ion exchange membrane is bowed or deformed.
2. Description of the Prior Art
In a highly miniaturized actuator, frictional and viscous forces dominate over inertial forces. Because of this, it is considered difficult to realize an ultra-small actuator using a motor, engine or other mechanism which converts energy to motion. The ultra-small actuators proposed up to now can be classified by operating principle into, inter alia, the electrostatic attraction type, piezoelectric type, ultrasonic type, shape-memory alloy type and polymer expansion type.
In the electrostatic attraction type actuator, plate or rod electrodes are attracted to each other. There have been developed actuators of this type in which a voltage of around 100 V is applied across two electrodes separated by dozens of .mu.m so as to cause one to bend toward the other. The piezoelectric type actuator has a piezoelectric element formed of a ceramic material, such as barium titanate, which is caused to expand and contract by the application of dozens of positive volts. Some are able to control displacement on the nanometer order. The ultrasonic type actuators include some driven by using a combination of frictional force and ultrasonic vibration produced by a piezoelectric element for causing the element to shift. The shape-memory alloy type actuator, which uses an alloy whose shape changes greatly with temperature, is driven by temperature variation. The polymer expansion type actuator uses a polymer fiber that expands and contracts with changes in temperature, pH or concentration of an ambient chemical substance.
However, all of the conventional ultra-small actuators have drawbacks of one sort or another. Some are limited as to the environment in which they can operate, others exhibit inadequate response or are overly complex in structure, and still others cannot be used in a living organism because they lack the pliancy required for ensuring that the living tissue will not be injured.
Even though the conventional polymer expansion type actuator does exhibit pliancy, its operation requires the solution in contact with the polymer fiber to be exchanged with another solution containing a salt, and therefore, it is not appropriate for use in applications requiring a miniature actuator with rapid response. While electrically driven polymer actuators have also been developed, they require a driving voltage at least as high as that at which electrolysis of water occurs, which makes them difficult to use in a living organism or other such closed system.
The object of the present invention is to provide an actuator element that is simple in structure, can be readily miniaturized, exhibits rapid response, operates at lower power and is pliant.